US3044556A - Screw propellers - Google Patents

Description

July 17, 1962 D. M. JEFFERSON SCREW PROPELLERS Filed May 9, 1958 WITNESSES. @Wi

90m 65 4x7444 I 3,044,556 SCREW PROPELLERS Donald M. .leflerson, Virginia Beach, Va, assignor to Clipper Propeller, Inc, Sykesville, Md., a corporation of Maryland Filed May 9, 1958, Ser. No. 734,370 2 Claims. (Q1. 170-159) This invention relates to a screw propeller, and it is especially adapted for marine transportation. Marine propellers today are so inelficient that the insertion of deviating planes in the propeller race has added considerably to the propeller performance. My propeller has for its particular object to discharge the propeller race directly backwards without any rotation whatever, which,

of course, makes it impossible to cause a higher pressure build-up by means of extraneous paraphernalia.

The results of many years of experimentation have evolved a standard wheel with uniform pitch and blades elliptical in shape set at right angles to the shaft, or slightly raked aft from the perpendicular, according to the individual fancy. In the propeller herein disclosed, nothing in the design is left to the individual fancy, and when the diameter and apparent pitch is decided upon the propeller becomes determinate in substantially every detail.

V Further, in my propeller, I prefer to incorporate blades having rhomboid blade sections, with a constant pitch for the opposite sides of the rhomboid, the pitch of the leading and trailing edges being substantially half of the apparent pitch of the face and back sides of the blades.

Finally, according to the invention, the width of the propeller blades varies with the distance from the center of the propeller, as the width of the active face equals the apparent pitch thereof multiplied by cosine for the inclination angle of the rhomboid element with the disc area of the propeller.

In the drawing:

Patented July 17, 1962 distance of the apparent pitch, but tends to be forced backwards through the water by the resistance to the ships forward movement. The screw propeller is a rigid unit so that any part thereof partakes of the backward relative motion which is equal for all the cylindrical sections of the propeller, and as long as the pressure on the face surface of the propeller does not exceed the atmospheric pressure, the propeller race will not rotate and the conditions are as illustrated in FIGURE 3.

FIGURE 3 shows the streamlined slip S of the propeller race. It is to be noted that the non-rotating slip layer in passing over the rotating blade must increase its velocity relative to the blade, therefore, the velocity 21rR increases to 21rR/cos a as shown in the diagram. In one revolution, a slip column 21r S has been accelerated backward a distance equal to the apparent pitch P, and inasmuch as the blades must at all times support the force needed to cause said acceleration in one revolution, and the amount of water in touch with the FIGURE 1 is a plan View of the propeller, showing the I ranged as shown. The propeller hub 3 has a tapered bore 4 to fit around the tapered shaft 10, which is preferably provided with a fairlead locknut 11. The blades are formed with their edges parallel with the generating lines 7, and the back and face sides of the blades are parallel with the generating lines 6, all as shown in the drawing. The outline 5 of the blade section shows an increase of thickness at the hub to withstand the bending moment on the blades.

The construction of the propeller will be understood from the following discussion. Fundamentally, the propeller does not travel forward the full distance of its pitch as the blades revolve, but is, in eifect, an inclined rotating plane, which plane does not advance the full active blade area multiplied by the slip acceleration must equal the total water column multiplied by the slip acceleration or:

or B=P cos a, where B is the width of a cylindrical blade section :at the radius R which has an inclination angle a to the propeller disc area. in the diagram FIG. 3 is the amassed blade width of the propeller, and it has to be divided by the number of l. A propeller having its blades composed of substantially rhomboid cylindrical sections, the apparent pitch of the back and the face surfaces of the blades being constant for the entire blade length, and the apparent pitch of the leading and trailing edges constant for the entire blade length and substantially equal to half that of the back and face surface of the propeller blades.

2. A propeller having its blades composed of substantially rhomboid cylindrical sections, the apparent pitch of the back and face surfaces of the blades being constant for the entire blade length, with the apparent pitch of the leading and trailing edges constant for the entire blade length and substantially equal to half that of the back and face surfaces of the propeller blades and the width of said cylindrical sections varying with the cosine value of their inclination angles with the disc area of the propeller.

References Cited in the file of this patent UNITED STATES PATENTS 832,173 'Iaylor Oct. 2, 1906 1,546,554 Ross r July 21, 1925 1,767,786 Engstrand June 24, 1930 2,097,389 De Mey et a1 Oct. 26, 1937 2,686,568 Engstrand Aug. 17, 1954 The blade width B

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